Na-ion batteries (NIBs) are proposed as a promising candidate for beyond Li-ion chemistries, however, a key challenge associated with NIBs is the inability to achieve intercalation in graphite anodes. This phenomenon has been investigated and is believed to arise due to the thermodynamic instability of Na-intercalated graphite. We have recently demonstrated theoretical calculations showing it is possible to achieve thermodynamically stable Na-intercalated graphene structures with a fluorine surface modifier. Here, we present experimental evidence that Na + intercalation is indeed possible in fluorinated few-layer graphene (F-FLG) structures using cyclic voltammetry (CV), ion-sensitive scanning electrochemical microscopy (SECM) and in situ Raman spectroscopy. SECM and Raman spectroscopy confirmed Na + intercalation in F-FLG, while CV measurements allowed us to quantify Na-intercalated F-FLG stoichiometries around NaC 14–18 . These stoichiometries are higher than the previously reported values of NaC 186 in graphite. Our experiments revealed that reversible Na + ion intercalation also requires a pre-formed Li-based SEI in addition to the surface fluorination, thereby highlighting the critical role of SEI in controlling ion-transfer kinetics in alkali-ion batteries. In summary, our findings highlight the use of surface modification and careful study of electrode-electrolyte interfaces and interphases as an enabling strategy for NIBs.
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Nanoscale Visualization of Reversible Redox Pathways in Lithium-Sulfur Battery Using In Situ AFM-SECM
Deducing the electrochemical activity of intermediates and providing materials solution to alter their reaction pathways holds the key for developing advanced energy storage systems such as lithium-sulfur (Li-S) batteries. Herein, we provide mechanistic perspectives of the substrate guided reaction pathways of intermediate polysulfides and their correlation to the redox activity of discharge end products using In Situ atomic force microscopy-based scanning electrochemical microscopy (AFM-SECM) coupled Raman spectroscopy at nanoscale spatiotemporal resolution. In Situ SECM intermediate detection along with Raman analysis at the electrode/electrolyte interface reveals that the precipitation of Li 2 S can occur via an electrochemically active lithium disulfide (Li 2 S 2 ) intermediate step. With a detailed spectro-electrochemical and morphological mapping, we decipher that the substrate-dependent Li 2 S 2 formation adversely affects the Li 2 S oxidation in the subsequent cycles, thereby reducing the round-trip efficiency and overall performance of the cell. The present study provides nanoscale-resolved information regarding the polysulfide reaction pathways in Li-S batteries with respect to the electrode structure and its properties.
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- Award ID(s):
- 1751472
- NSF-PAR ID:
- 10391934
- Date Published:
- Journal Name:
- Journal of The Electrochemical Society
- Volume:
- 169
- Issue:
- 6
- ISSN:
- 0013-4651
- Page Range / eLocation ID:
- 060501
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1149/1945-7111/ac70ff
